A surveying instrument, for example, a total station includes a telescope that collimates a measurement point, a bracket portion that supports the telescope rotatably in the vertical direction, and a base that supports the bracket portion rotatably in the horizontal direction. The telescope is driven by a vertical rotary motor provided on a vertical rotary shaft, and the bracket portion is driven by a horizontal rotary motor provided on a horizontal rotary shaft. Patent Document 1 discloses a surveying instrument adopting ultrasonic motors as the vertical rotary motor and the horizontal rotary motor.
It is difficult for an ultrasonic motor to rotate at a low speed during continuous driving. Therefore, at the time of low-speed rotation, as shown in FIG. 10, intermittent driving by turning ON/OFF a drive signal is performed. That is, in a drive cycle TM, an acceleration period Ta in which the drive signal is applied and a deceleration period Tr in which the drive signal is stopped are provided, and by changing a ratio of the acceleration period Ta and the deceleration period Tr, an average speed in the drive cycle TM is controlled.
Many surveying instruments have a function of automatically tracking a moving target as disclosed in, for example, Patent Document 2. There is a method for automatically tracking in which a surveying instrument is provided with a light emitting unit that irradiates tracking light and a light receiving unit that receives reflected light of the tracking light, a lighted image and an unlighted image are acquired and a difference between these is obtained, and a position with a deviation falling within a predetermined value from the center of a visual axis of the telescope is detected as a target position.